This invention relates generally to turbomachinery compressors and more particularly relates to centrifugal stages of such compressors.
A gas turbine engine includes, in serial flow communication, a compressor, a combustor, and turbine. The turbine is mechanically coupled to the compressor and the three components define a turbomachinery core. The core is operable in a known manner to generate a flow of hot, pressurized combustion gases to operate the engine as well as perform useful work such as providing propulsive thrust or mechanical work.
One known configuration of the compressor is the “axi-centrifugal” compressor which includes an upstream axial-flow portion that discharges to a downstream centrifugal-flow portion. In some designs it is desirable to have a relatively large radius at the inlet of the centrifugal-flow portion. However, because stresses due to speed scale with the square of the ring radius, relatively small increases in radius can result in significant increases in hoop stresses in the centrifugal impeller near its attachment to the axial-flow portion. The result is that the centrifugal impeller, due to its combination of radius and wheel speed, cannot self-support its own speed induced-loads. Prior art connection methods between the two compressor portions, including CURVIC face couplings and bolted joints, cannot operate at this high a radius and wheel speed with acceptable stress levels.
Accordingly, there remains a need for an axi-centrifugal compressor that is operable with at a high radius and wheel speed, with acceptable stress levels.